A chip of a semiconductor device is incorporated as a switching device for a power conversion apparatus. Silicon (Si) has been generally used as a material for a semiconductor device. For example, for a large capacity load such as a drive apparatus for a railway vehicle, an insulated gate bipolar transistor (IGBT) is used as a switching device from the point of view of the breakdown voltage and the current capacity. On the other hand, in recent years, research and development of semiconductor devices for which a wideband gap semiconductor such as silicon carbide (SiC) which is a compound semiconductor is used as a material have been and are being promoted. For example, development of a metal oxide semiconductor field effect transistor (MOSFET) (hereinafter referred to as SiC-MOSFET) for which SiC which has a breakdown voltage similar to that of a silicon IGBT (Si-IGBT) and whose electric resistance upon conduction can be reduced is being performed actively.
As one of characteristics of a switching device, a threshold voltage is available. The threshold voltage is a gate voltage when more than current of a fixed level flows through the switching device. For example, although an re-channel MOSFET normally is in an off state, if a positive voltage equal to or higher than the threshold voltage is applied to the gate, then the n-channel MOSFET is placed into an on state.
Patent Document 1 indicates that, where a wideband gap semiconductor is utilized for a semiconductor switching device, since a high temperature environment is required upon fabrication, it is difficult to stably fabricate the semiconductor switching device and an individual dispersion exists in the gate threshold voltage, and discloses a technology for reducing leak current of a switching device by controlling the driving voltage on the basis of a detection value of leak current of the switching device against the individual dispersion of the gate threshold voltage.